A 65-year-old woman is brought to the physician due to 6 months of dry cough and worsening dyspnea. Her dyspnea has progressed so that she is now able to walk only a few steps. She has no fever, chest pain, or hemoptysis. Her only medication is hydrochlorothiazide for hypertension. The patient is a retired schoolteacher and does not use tobacco or alcohol. She has no pets and has never traveled abroad. Temperature is 37.2 C (99 F), blood pressure is 140/86 mm Hg, pulse is 84/min, and respirations are 18/min. Chest examination shows dry, late inspiratory crackles and digital clubbing. There is no peripheral edema. Serology is negative for antinuclear antibodies and antineutrophil cytoplasmic antibodies. Chest x-ray shows diffuse reticular opacities. A high-resolution computed tomography scan is shown below.
Show Explanatory Sources
Which of the following abnormalities is most likely to be present in this patient?
Interstitial lung disease | |
Common etiologies |
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Clinical presentation |
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Diagnosis |
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DLCO = diffusion capacity of the lung for carbon monoxide; HP = hypersensitivity pneumonitis; | |
This patient's presentation is consistent with pulmonary fibrosis due to interstitial lung disease (ILD). ILD can be due to known causes (eg, infections, connective tissue disease) or may be idiopathic (eg, idiopathic pulmonary fibrosis, cryptogenic organizing pneumonia). Patients typically have progressively worsening exertional dyspnea and/or persistent dry cough. Examination can show fine crackles during mid-late inspiration and sometimes digital clubbing. Chest x-ray often shows reticular or nodular interstitial opacities and high-resolution chest CT usually demonstrates fibrosis, honeycombing, and traction bronchiectasis. The diagnosis is based on clinical features, pulmonary function testing, and radiographic imaging. However, lung biopsy may be required in patients who have an unclear diagnosis after initial assessments. Those without an identifiable environmental, infectious, or autoimmune etiology, as is likely the case with this patient, are typically diagnosed with idiopathic pulmonary fibrosis (IPF).
In ILD, there is excessive collagen deposition in the extracellular matrix around the alveoli, which decreases diffusion capacity (Choice C) across the alveolar-capillary membrane, increasing the alveolar-arterial oxygen gradient and causing hypoxemia. The scarring and fibrosis reduce total lung capacity, functional residual capacity, and residual volume (Choice E). The fibrosis also increases elastic recoil in the airways and results in a restrictive pattern on pulmonary function testing. FEV1 and FVC are both decreased, but because the decrease in FVC is greater, the ratio is either normal or increased (Choice A).
(Choice D) Hypercapnia (increased PaCO2) is typically a late finding in ILD, in part because CO2 diffuses across the alveolar-capillary membrane much more rapidly than O2. In addition, in contrast with the air trapping that occurs with obstructive lung disease (eg, emphysema), CO2 is more readily exhaled from the alveoli in restrictive lung disease. In ILD, hypoxemia, especially with exertion, is more characteristically observed than hypercapnia.
Educational objective:
Interstitial lung disease (eg, idiopathic pulmonary fibrosis) involves excessive collagen deposition in the perialveolar tissues. This leads to decreased diffusion capacity across the alveolar-capillary membrane, increasing the alveolar-arterial oxygen gradient and causing hypoxemia. Pulmonary function testing shows a restrictive pattern (ie, decreased FEV1 and FVC with the FEV1/FVC ratio normal or increased).